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average water level


sjorat
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After creating a contour map of water levels, or for the matter any other parameter, can I get the statistics (average, max, min, . . . ) of that parameter within a given polygon? I need to get the average water level with certain parcel of land. I thought this should be relatively easy within GMS, as most the work is already done by creating the contour map and also drawing a polygon. Thx;

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If you have your polygon in a coverage that you want the values from, you could go through the following steps to get the average, min, and max.

- With the 3D grid module selected, select the Edit | Datset Calculator menu item.

- In the Expression field enter 0.0, name the Result field mask and select the Compute button.

A data set called mask is created with all of the values set to zero. Now we need to set the values in the cells we are interested in to 1.0.

- Select the coverage containing the polygon in the Project Explorer.

- Right click on the polygon in the graphics window and select Select Intersecting Objects from the popup menu.

- In the dialog that comes up select 3D Grid Cells.

- Select the mask data set in the Project Explorer.

- Change the dataset value of all of the selected cells to 1.0 by entering 1.0 for the F: field above the graphics window and press the enter key.

Now that we have a dataset that has ones everywhere we are interested in we can use the data calculator to create data values in the area we are interested in.

- Select the Edit | Datset Calculator menu item.

- In the Data sets tree, double click on the mask dataset to enter it in the expression.

- Click on the "*" button to multiply.

- Double click on the dataset you want the values from (for instance Head from the MODFLOW solution).

- Name the result dataset (for this we could call it Head Poly Values), select the Compute button.

- Select the Done button to exit the data calculator.

We now have a dataset with head values we're interested in and zeros everywhere else.

- Right click on the Head Poly Values dataset in the Project Explorer and select Properties.

The dataset info window includes the max, min, and mean but it also includes the portion of the grid with zeros in the calculation.

- Select the Edit Inactive Flags button. The dialog should already have 0.0 entered as a value.

- Select the OK button to inactivate the cells with 0.0 values.

The max, min, mean, etc. in the dataset info window should be updated to include only the cells we're interested in.

It would be nice if this were simpler. Maybe with an option to show only selected cells in the dataset info window.

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